This invention relates to a method for reinforcing a wooden truss using a reinforcement device comprising a bracket which is mounted on a principal rafter of the truss and anchored to the truss.
In the construction of buildings, it is common practice to construct a roof of a building by suspending wood trusses between respective top ends of opposing pairs of load bearing walls of the building. Each truss is an elongate structure having a principal rafter with mounting portions at respective ends thereof. The mounting portions extend past respective ends of the truss for being supported on the respective load bearing walls. Generally a small bearing offset between one or both ends of the truss and the corresponding load bearing wall is permitted, however if this offset is too large, the strength of the truss becomes significantly reduced and premature failure may occur. It is generally not known however if the bearing offset is within, tolerance until the truss has been assembled and installed. To ensure that the truss meets its design strength, the truss must then be reconstructed if the bearing offset is too great, which involves an undesirable waste of material and labour.
According to one aspect of the present invention there is provided a reinforcement device for use with an elongate wooden truss having a principal rafter extending longitudinally with the truss and past respective ends thereof, the device comprising:
a channel for receiving the principal rafter therein;
channel mounting means for mounting the channel on the principal rafter such that the principal rafter is engaged therein;
a rigid anchor secured to the channel and extending outwardly therefrom;
and anchor mounting means for mounting the anchor on the truss.
When an elongate truss having a principal rafter extending past respective ends of the truss is mounted on a supporting structure and the bearing offset exceeds a recommended tolerance, the reinforcement device of the present invention can be mounted on the truss to ensure that the truss meets its design strength. The device is mounted on the truss by securing the channel on the principal rafter between an end of the truss and the supporting structure supporting a corresponding end of the principal rafter thereon such that the channel spans the bearing offset therebetween. By subsequently securing the anchor to the truss, for example one of the struts of the truss, the reinforcement device provides torsional and load bearing support between the end of the principal rafter and the end of the truss to assist the truss in meeting its design strength.
There may be provided a mounting face on the anchor for engaging a side of the truss, wherein the channel includes an engaging face which extends perpendicularly to the mounting face for engaging a top side of the principal rafter. The orientation of the engaging face permits at least a portion of the channel to be supported on a top side of the rafter such that the channel mounting means do not support the entire load transferred between the rafter and the channel. When the channel mounting means comprises a set of fasteners for example, the fasteners are not required to support the entire load in shear.
Preferably, the channel has a C-shaped cross section including a base member and a pair of side flanges extending therefrom which are parallel and spaced apart for engaging opposing sides of the principal rafter such that the rafter is secured therebetween. The channel is thus able to transfer torsional loads between the principal rafter and the truss without relying on the channel mounting means due to the secure fit of the rafter within the channel which is engaged on three sides thereof.
When there is provided a mounting face on the anchor for engaging a side of the truss, the channel is preferably oriented such that the base member is substantially parallel to the mounting face of the anchor. The orientation of the channel ensures that at least portion of the channel is arranged to be supported on the top side of the rafter for assisting the channel mounting means in transferring loads from the principal rafter to the truss.
The anchor mounting means are preferably spaced from the channel. The spacing of the anchor mounting means from the channel assists in transferring torsional loads from the channel to the truss while subjecting the anchor mounting means to minimal stress therefrom.
The channel and the anchor preferably comprise an elongate rectangular plate which has been bent to define the channel and the anchor respectively. The device is thus simple to manufacture at minimal cost.
The channel mounting means and the anchor mounting means preferably comprise at least one aperture in the channel and the anchor respectively for receiving a corresponding fastener therethrough. The use of fasteners, for example screws or bolts, allows the reinforcement device to be readily installed in the field using conventional tools.
According to a second aspect of the present invention there is provided a truss for supporting a roof on a supporting structure, the truss comprising:
an elongate frame structure;
a principal rafter extending longitudinally with the frame structure and past respective ends thereof, defining a pair of mounting portions located at respective ends of the principal rafter for supporting the rafter on the supporting structure;
a channel mounted on one of the mounting portions of the principal rafter and securing the rafter therein; and
a rigid anchor extending between and secured to the channel and the frame structure.
There may be provided a channel mounted at each end of the principal rafter, each channel having an anchor mounted thereon for coupling to the frame structure.
When the frame structure includes a plurality of struts such that an outermost pair of the struts define the respective ends of the frame structure, the anchor is preferably mounted on one of the outermost struts. The outermost struts may each comprise an upright post or an inclined support member.
The channel preferably comprises a clamp member of C-shaped cross section having a base and a pair of flanges extending therefrom for engaging respective sides of the principal rafter.
The channel preferably includes an engaging face which is engaged on a top side of the principal rafter.
According to a further aspect of the present invention there is provided a method of reinforcing an elongate truss having an elongate principal rafter extending longitudinally with the truss past respective ends of the truss, the method comprising:
providing a bracket having a channel arranged to receive the principal rafter therein and an anchor for anchoring the bracket on the truss;
mounting the channel on the principal rafter between an end of the truss and an end of the rafter; and
mounting the anchor on the truss.
The method preferably includes mounting the channel on the rafter such that a portion of the channel engages a top side of the rafter.
When the truss includes a plurality of struts coupled to the principal rafter, the method preferably includes mounting the anchor on an outermost strut adjacent the corresponding end of the rafter mounting the channel thereon.
When the principal rafter is supported at respective ends on a supporting structure, the method preferably includes selecting a channel having a width which is substantially equal to a spacing between one end of the truss and the supporting structure before the channel is mounted therebetween.